Surface coatings can provide medical articles, such as those that are implanted or temporarily inserted into the body, with a variety of distinct benefits. These benefits include lubricity and wettability, passivity against protein absorption, antimicrobial properties, drug delivery, biocompatibility, and hemocompatibility. The demand for medical articles having these types of coatings is rapidly increasing because they generally improve the function of the device upon implantation or insertion in the body.
Coatings that have lubricious and wettable properties typically include hydrophilic materials. These hydrophilic materials reduce frictional forces when the device is introduced and moved within the body. Various catheter types are examples of medical articles that may be provided with hydrophilic coatings. Hydrophilic coatings are generally known in the art of implantable medical devices.
Providing hydrophilic coatings to medical devices can be particularly challenging from many standpoints. Many medical devices are twisted or contorted during use of the device in the body, which may result in cracking, or peeling of the coating. In addition, since hydrophilic coatings have the potential to swell to a certain extent in an aqueous environment, the components of the coating can potentially become dislodged and lost from the coating if not sufficiently stabilized. Given these factors, the coatings should adhere sufficiently to the device. Further, the dimensions and modulus of the device can be affected by coatings that are excessively thick. However, preparation of thin hydrophilic coatings can be difficult as a result of the properties of components that are used in the coating process.
Further, coatings are often prepared using organic solvents or low molecular weight monomeric compounds, which in some cases present toxicity concerns. While it is generally desirable to remove all solvent or unreacted low molecular weight monomeric materials, these components may remain in the coating in trace amounts. It is often necessary to properly handle these materials and remove them if they remain in the formed coating.
In addition to the general technical difficulties of producing a hydrophilic coatings that are compliant and durable, it can be difficult to keep a coated article sufficiently hydrated for a period of time prior to use. This period of time, generally commencing after removing the device from a wetting solution and before the device is inserted into a patent is referred to as “open time.” During this period of time coatings can become dried out, resulting in discomfort to the patient upon insertion of the device. The drying may prompt rewetting of the coating, which, aside from adding to the insertion process, can increase the risk of infection.
In addition to those issues associated with device coating, in many cases it is desired to perform sterilization procedures on coated medical devices. Common sterilization procedures for medical devices include treating the device with ethylene oxide. However, coated polymeric materials can be sensitive to sterilization procedures, which may damage the coating by causing it to delaminate from the surface of the device or may alter the chemical properties of materials in the coating. For example, ethylene oxide sterilization can cause alkylation of the hydrophilic polymeric materials and greatly reduce the lubricity of the device.